Ultrasound imaging has found wide application in many clinical specialties. Real time volumetric imaging (RT3D) promises to play an important role in image-guided interventions. Intervascular (IVUS) and intravascular (ICE) ultrasound has also found important clinical applications. They propose to further enhance the capabilities of these new modalities. To date, IVUS and ICE are tomographic techniques permitting only sectional views of artheroscloratic plaque or the myocardial walls. Imaging the entire vessel geometry near a plaque or by visualizing an extended patch of the myocardium will enhance utility. RT3D combined with real time rendering now permits catheter-based ultrasound visualization analogous to that obtainable with fiber optics. Current implementations evidence poor image quality. The forward-looking 2D arrays are too large to access smaller vessels (e.g., coronary arteries), and they suffer from lack of sensitivity, undersampling of the array, and high production costs. To overcome these limitations, they propose a two-stage development for unique 2D arrays based on MEMS processing technology to be integrated with advanced custom circuits. In Phase 1, we will construct, evaluate, and optimize unique multilayer 10-30 MHz transducer arrays operating in the flexure rather than the thickness mode. In Phase 2 they propose the construction and evaluation of 6F catheters with forward-looking 2D arrays with over 300 active elements. In vitro and limited in vivo tests are proposed and the catheter will be interfaced with an extant RT3D system. The proposed multilayer integrated array methodology can also be applied to non-invasive RT3D to significantly improve image quality. High quality forward-looking catheter based ultrasound imaging will permit cardiovascular navigation and allow assessment of plaque location and size, cardiac morphology, and myocardial pathology. It will aid in the placement of other devices such as pacing wires and will permit on-line visualization of cardiac interventions such as ablation therapy. The development of improved 2D arrays is essential to the realization of the full potential of RT3D in diagnosis and in the vital new area of image guided therapies.